▎ 摘　　要

Graphene possesses large Kerr nonlinearities that enabled the realization of energy-efficient nonlinear optical devices. At the same time, electronic scattering of graphene plasmons shows very high energy transfer efficiencies at very low beam energies due to its extremely large plasmon wave vector. We have tapped into these two unique optical properties of graphene to study the potential of an energy-efficient optoelectronic light source and all-optical modulator. We found that 2 pi-phase shift and 94% loss modulation is achievable with just a 25.6-V electron beam passing 10 nm above a graphene waveguide with a Fermi level of 0.1 eV. This also enables nonlinear optical devices to utilize in situ generated plasmons without the need of external optics, which could herald the return of vacuum nanoelectronics.